We have investigated the pretreatment effects of nitrogen on the length and the alignment of
carbon nanotubes (CNTs) grown on a Ni catalyst by using dc-plasma enhanced chemical vapor deposition
system. The surface of the Ni catalyst was pretreated with a mixture of NH3 and N2, instead of pure NH3
and the length of the CNTs has changed from 1.6 ?m to 400 nm as the NH3/N2 flow rate ratio was
decreased. We showed that the length and the alignment of the CNTs could be controlled by changing the
NH3/N2 flow rate ratio. The fabricated CNTs were further evaluated by using their Raman spectra. The
nitrogen concentration on the surface of the Ni catalyst after the pre-treatment was analyzed by using X-ray
photoelectron spectroscopy and the physical structure of CNTs was analyzed using scanning electron
microscopy and high resolution transmission electron microscope. We suggest that the N2 adsorption on the
surface of Ni changes the carbon atom diffusion during the CNT growth and that the physical structures of
CNTs are drastically changed.
